Qt只启动一个exe的QSingleApplication

有些项目只允许启动一个exe，因此需要处理一下，Qt自己给了一个QSingleApplication的例子

使用QLocalServer创建一个服务，然后每次启动时，判断是否已经有连接上，具体代码如下

#ifndef SINGLE_APPLICATION_H
#define SINGLE_APPLICATION_H

#include <QApplication>

class QLocalServer;

class QSingleApplication : public QApplication
{
    Q_OBJECT

public:
    QSingleApplication(int argc, char **argv);
    // 判断进程是否存在
    bool isRunning();

private slots:
    void newLocalConnection();

private:
    QLocalServer *pServer;
    bool bRunning;
};

#endif // SINGLE_APPLICATION_H

#include "qsingleapplication.h"
#include <QLocalSocket>
#include <QLocalServer>
#include <QFile>
#include <QTextStream>

QSingleApplication::QSingleApplication(int argc, char **argv)
    : QApplication(argc, argv),
      bRunning(false)
{
    QCoreApplication::setApplicationName("BPaaa");
    QCoreApplication::setApplicationVersion("VERSION_STRING");
    QCoreApplication::setOrganizationName("BPabc");
    QCoreApplication::setOrganizationDomain("https://github.com");
    QString strServerName = QCoreApplication::organizationName() + QCoreApplication::applicationName();

    QLocalSocket socket;
    socket.connectToServer(strServerName);

    if (socket.waitForConnected(500))
    {
        QTextStream stream(&socket);
        QStringList args = QCoreApplication::arguments();

        QString strArg = (args.count() > 1) ? args.last() : "";
        stream << strArg;
        stream.flush();
        qDebug() << "Have already connected to server.";

        socket.waitForBytesWritten();

        bRunning = true;
    }
    else
    {
        // 如果不能连接到服务器，则创建一个
        pServer = new QLocalServer(this);
        connect(pServer, SIGNAL(newConnection()), this, SLOT(newLocalConnection()));

        if (pServer->listen(strServerName))
        {
            // 防止程序崩溃，残留进程服务，直接移除
            if ((pServer->serverError() == QAbstractSocket::AddressInUseError) && QFile::exists(pServer->serverName()))
            {
                QFile::remove(pServer->serverName());
                pServer->listen(strServerName);
            }
        }
    }
}

void QSingleApplication::newLocalConnection()
{
    QLocalSocket *pSocket = pServer->nextPendingConnection();
    if (pSocket != nullptr)
    {
        pSocket->waitForReadyRead(1000);

        QTextStream in(pSocket);
        QString strValue;
        in >> strValue;
        qDebug() << QString("The value is: %1").arg(strValue);

        delete pSocket;
        pSocket = nullptr;
    }
}

bool QSingleApplication::isRunning()
{
    return bRunning;
}

使用方式如下

int main(int argc, char *argv[])
{
//    QApplication a(argc, argv);   //替换掉这一句
    QSingleApplication a(argc, argv);
    if(a.isRunning())
    {
        return 0;
    }
......
......
    return a.exec();
}

也有用QShareMemory处理的,在main.cpp中加入如下语句。

    QSystemSemaphore sema("AA",1, QSystemSemaphore::Open);
    sema.acquire();// 在临界区操作共享内存   SharedMemory
    QSharedMemory mem("AAAAA");// 全局对象名
    if (!mem.create(1))// 如果全局对象已存在则退出
    {
        sema.release(); // 如果是 Unix 系统，会自动释放。
        return 0;
    }